Many electronic cameras are used at night or other dim-light situations. These include some camcorders, security cameras, trail cameras, digital night-vision goggles and gunsights, dashcams, and similar products that are often fitted with an invisible, infrared, light source. The infrared source often allows imaging in low light without disturbing or alerting people or animals. While it is desirable for these cameras to resolve color images when bright natural light exists, high sensitivity to infrared light is particularly important for these applications.
Traditional front-side illuminated (FSI), 4-color, red, green, blue, and infrared (RGB-IR) color photosensor arrays typically use a filter matrix having a tiling unit 100 as illustrated in FIG. 1 having at least one red 108, green 104, blue 102, and infrared 106 bandpass filter, where each filter is located over a photosensor. In some embodiments where the blue 102, green 104, and/or red 108 visible-light color filters are partially or fully transparent to infrared light and low crosstalk is desired, a visible-light-passing, infrared blocking filter 109 is added ahead of one or more of visible light color filters 102, 104, 108 at cost of an extra masking step and of reducing sensitivity to infrared light. Traditional FSI RGB-IR photosensor arrays, as illustrated in FIG. 2, also have a blue-detecting N-type diffusion 110, a green-detecting N-type diffusion 112, an infrared-detecting N-type diffusion 114, and a red-detecting N-type diffusion 116 formed into an upper surface of a P-type epitaxial layer 120, in a particular embodiment the P-type epitaxial layer is doped to ten ohms-centimeter resistivity. Each of the N-type diffusions 110, 112, 114, 116 is diffused to the same depth, and form a photodiode junction with the epitaxial layer 120. The N-type diffusions are separated from each other by grounded, P-type, barrier regions 122, 124 that also serve as ground contacts to the epitaxial layer 120. In some, but not all, systems, epitaxial layer 120 is grown on a grounded substrate 126.
Each photodiode 150 (FIG. 3), such as the photodiodes formed by the N-type diffusions 110, 112, 114, 116 with the epitaxial layer 120, is coupled through a selection transistor 152 controlled by a row selection line 153 into precharge and sensing devices 154. Precharge and sensing devices 154 are as known in the RGB photosensor array art, and drives column data line 156.